Definition of Spatial Scales
Plot scale: areas of 100 to 102 m
Small experimental watershed: drainage area up to 5 km2
Large watershed: drainage area up to hundreds of square kilometers that drains to a reservoir or lake that is part of the water supply infrastructure
Landscape: collections of several large watersheds
Region: multiple municipal areas, each of which has its own water supply
In the early twenty-first century, water and resource managers are asking questions that challenge forest hydrologists to go beyond general principles and study designs of the past to make predictions and respond to emerging issues. These include, for example, questions about cumulative watershed effects in large watersheds, legacy effects of roads on peak flows and sediment movement, or direct and indirect effects of climate change on forest hydrologic processes. The present body of knowledge provides a foundation for answering these questions, but there are significant information gaps and research needs, described later in this report (see Chapters 3 and 4).
These issues and questions are the centerpiece of the tensions in basins around the country. Scientists, managers, and the citizenry are looking for new approaches to more fully understand watersheds, make stronger connections between forests and water, and achieve multiple stakeholder goals.
The Department of the Interior Assistant Secretary for Water and Science initiated discussions in 2005 with the Water Science and Technology Board (WSTB) of the National Academies’ National Research Council (NRC) for an assessment of the science of forest hydrology and how it relates to hydrologic effects of forest management practices. The USFS joined these discussions at the end of that year. Together, the U.S. Bureau of Reclamation and the USFS requested that the WSTB convene a committee to produce a report on the comprehensive understanding of forest hydrology, connections between forest management and attendant quality and quantity of streamflow, and directions for future research and management needs. In early 2006, the WSTB formed the Committee on Hydrologic Impacts of Forest Management, a panel of 14 members with expertise in forest hydrology and ecology, fire ecology, watershed sciences, geomorphology, water quality, and forest management on public and private land ranging from small woodlots to extensive industrial holdings (see Appendix B). The overall charge to the NRC committee was to examine the effects of forest management on water resources (see Box 1-2). The committee held five meetings between March 2006 and April 2007 in open and closed sess-